The present invention relates to an improvement on sealed lead-acid batteries using tubular positive plates. In particular, the present invention relates to a sealed tubular lead-acid battery having improved discharging performance and a longer cycle life.
In tubular positive plates, the active material for the positive electrode is encased in a tube and compressed from every side so that it will not be shed during charge and discharge cycles. Thus, lead-acid batteries using tubular positive plates are generally known to have a better cycle life performance than those using pasted electrode plates. It is also known that such tubular lead-acid batteries can be sealed by causing in situ gelation of a dilute sulfuric acid solution to which an inorganic oxide such as SiO.sub.2 or Al.sub.2 O.sub.3 has been added.
The gelled electrolyte described above has the sulfuric acid content immobilized within the gel so tightly that it will not diffuse easily. Hence, the discharge capacity of batteries using this electrolyte is significantly lower than that of conventional opened liquid electrolyte type batteries, especially during high-rate discharge. Further, as the battery is subjected to repeated charge and discharge cycles, a crack or a large hole will form in the gelled electrolyte to reduce the contact area with the positive plate. If this occurs, the positive active material will deteriorate rapidly since it undergoes local charge and discharge at a high current density. Thus, batteries using a gelled electrolyte have suffered the disadvantage that their cycle life performance is greatly inferior to that of batteries using a liquid electrolyte.